Method for lubricating at least two units of a vehicle equipped with an internal combustion engine

ABSTRACT

The present invention relates to a method for lubricating at least two units of a vehicle having an internal combustion engine, each unit comprising one or more assemblies, and to a corresponding vehicle. In order to be able to dispense with an oil change of the individual units, and at the same time ensure the necessary quality and quantity of lubricant, it is proposed according to the invention to conduct the lubricant in series through the at least two units in that fresh lubricant is fed to the first unit from a container, at least some of the used lubricant is removed from the oil trough of the individual units and is fed to the unit which is respectively arranged afterwards in the series, and the lubricant which is removed from the oil trough of the last unit is fed to the internal combustion engine for combustion.

The present invention relates to a method for lubricating at least twounits of a vehicle having an internal combustion engine, each unitcomprising one or more assemblies, and to a corresponding vehicle.

In conventional vehicles with an internal combustion engine, theindividual assemblies such as the transmission, engine, hydraulics, wetbrakes, retarders and the like are lubricated in closed lubricantcircuits which are separated from one another. In order to ensureoptimum lubrication of the lubrication points of the individualassemblies, different lubricants based on mineral oils or partially orcompletely synthetic fluids, which are adapted to the respectivetechnical lubrication requirements of the individual assemblies byadding special additives, are generally used for the various lubricationcircuits.

In order to reduce the number of different lubricants which arenecessary as a result of this, recently universal lubricants which aremainly suitable for agricultural and forestry vehicles, for example UTTO(Universal Tractor Transmission Oil) and STOU (Super Tractor OilUniversal), which can be used for lubricating a plurality of assemblies,have been developed. Whereas UTTO products can be used for lubricatinghydraulics, transmission and wet brakes, STOU oils are also suitable forlubricating engines. By using such universal lubricants it is possibleto supply a plurality of assemblies, such as hydraulics, transmissionand wet brakes, with a lubricant from a common lubricant circuit, whichlubricant is however structurally separated from the lubricant circuitof the internal combustion engine owing to the different requirementsmade in terms of the purity of the lubricant. Accordingly, such vehicleshave two separate units which are supplied by one isolated lubricantcircuit in each case, specifically on the one hand a unit which iscomposed of the assemblies comprising the hydraulics, transmission andwet brakes, and on the other hand the internal combustion engine.

All these systems have in common the fact that an oil change has to becarried out at the individual lubricant circuits at chronologicalintervals because, during the consumption, active ingredients are used,and the lubricant ages and is contaminated with extraneous substances.However, during an oil change, dangerous quantities of waste oil areproduced which have to be disposed of at some cost in accordance withtheir waste rating. In addition, each oil change inevitably requires thevehicle to be stationary for a time and incurs maintenance costs. Inaddition, in vehicles with a plurality of lubricant circuits, differentoil change intervals are often necessary and it is necessary to fill thecircuits with different lubricants, making the logistics of an oilchange more difficult.

In order to be able to dispense with at least one oil change of theengine lubricant circuit, it has recently been proposed to burn usedlubricant continuously or at intervals together with the fuel in theengine. With this type of waste lubrication, use is made of the factthat up to several percentages of oil can be added to the fuel of theinternal combustion engine without adversely affecting the performanceof the engine, said oil then being burnt along with the combustion offuel.

DE 31 38 144 A 1 discloses a lubricant and fuel circuit, in particularfor the diesel engines of heavy goods vehicles, in which a givenquantity of lubrication oil is periodically extracted from the oiltrough of the engine and fed to the fuel tank in order to burn theextracted quantity together with the customary diesel fuel in theengine. Furthermore, an automatically operating arrangement formonitoring the lubricant level is provided in order to keep it at a setpoint level in the oil trough so that freshly lubricant oil iscontinuously fed into the lubricant circuit and at the same time thewaste oil is periodically cleaned. Only one engine oil change whichgenerally takes place at intervals is therefore avoided by virtue of thefact that a specific quantity of used engine oil is continuouslyreplaced by a corresponding quantity of fresh engine oil, and the usedengine oil is burnt with the fuel.

DE 30 19 877 A1 discloses a device for changing oil in an internalcombustion engine with a lubrication system and an oil trough and a fuelsystem with a fuel tank in which, in order to change the oilautomatically and conduct away used lubricant, oil feeding means fortransferring some of the used engine oil from the lubrication system tothe fuel system are provided in order to mix the used proportion of oilwith fuel. Furthermore, the device has an oil tank for storing fresh oilas well as an oil supply means for supplying fresh oil from the oil tankto the lubrication system.

DE 30 06 903 A1 discloses a method for replacing the lubrication oilcollected in the oil sump of an internal combustion engine, using an oildischarge pump which has to be controlled separately, in which methodthe oil discharge pump adds metered quantities of oil from the oil sumpof the internal combustion engine to the fuel of the internal combustionengine and at least the quantity of fresh oil which corresponds to thedischarged quantity of oil is fed to the internal combustion engine.Here, the quantities of oil are dimensioned in such a way that theprescribed oil filling quantity is discharged independently of the oilconsumption of the internal combustion engine within an oil changeinterval. The control device is configured in such a way that the oildischarge pump begins to operate only during a fuel filling processduring which the filling level measuring display moves upward within ashort time.

Finally, WO 99/23365 discloses a method for lubricating andsimultaneously supplying fuel to the internal combustion engine in whicha plant oil which has been treated with additives is continuously fed aslubricant to the internal combustion engine during operation, and theused plant oil lubricant is metered, together with a mixture of freshplant oil and diesel oil or rape seed oil methyl ester in the engine,and burnt as engine fuel.

Although these methods make it possible to dispense with an oil changeof the engine lubrication circuit, the lubricants for the otherassemblies such as the transmission, hydraulics and the like have to bereplaced at regular intervals with the associated disadvantages. Afurther disadvantage of these methods is the logistical expenditure onsupplying fresh lubricant to the individual lubrication circuits whichare separated from one another.

The object of the present invention is therefore to make available amethod for lubricating all the fluid-lubricated units, however at leasttwo units of a vehicle having an internal combustion engine, in which anoil change is not necessary for the respective units, and neverthelessthe necessary quality and quantity of lubricant is ensured.

This object is essentially achieved with a method of the type mentionedat the beginning in that the lubricant is successively conveyed throughat least two units, in that fresh lubricant is fed to the first unitfrom a container, at least some of the used lubricant is removed fromthe oil trough of the individual units and fed to the unit which isrespectively arranged afterwards in the series, and the lubricant whichis removed from the oil trough of the last unit is fed to the internalcombustion engine for combustion.

Owing to the common lubrication of all the units with a lubricant andsubsequent thermal recycling of the waste oil in the engine, with themethod according to the invention an oil change is no longer necessaryin the respective units so that costly disposal of waste oil isdispensed with, and the stationary times of the vehicle which resultfrom this are avoided. In addition, all that is now necessary is to feedfresh oil to the first unit in the series so that the logisticalexpenditure is considerably reduced. Apart from the maintenanceadvantages and the simplified logistics for the operator, this methodensures that, on the one hand, during operation, fresh, or at mostlightly aged lubricant which is still suitable for lubrication, is fedcontinuously to all the units, and, on the other hand, aged lubricant iscontinuously removed from these lubrication circuits so that a lubricantwhich is sufficiently fresh is always available in all the lubricationcircuits for optimum lubrication of the lubrication points. Here, therefreshing rate, that is to say the proportion of the fresh lubricantwhich is fed to the units and of the used lubricant which is removedfrom the lubrication circuits, with respect to the fuel consumption, canbe adapted to the quality of the used lubricant and to the loading towhich the lubricant is subjected overall in all the units.

The refreshing rate is preferably between 0.1% and 2.5%.

Furthermore, the units are preferably arranged in accordance with thedegree of their requirement for purity of the lubricant. This ensuresthat the unit with the highest requirement of purity is fed with freshlubricant while the lubricant supply of the units with lowerrequirements is refreshed with partially aged lubricant from the unitwhich was respectively arranged in the preceding position in the seriesbefore the used lubricant is then burnt in the internal combustionengine at the end of the use chain.

In a tractor with two separate lubrication circuits, specifically onefor hydraulics, transmission and wet brakes and one for the engine, forexample fresh lubricant is preferably firstly fed to the unit composedof hydraulics, transmission and wet brakes, since in said unit thepurity of the lubricant, a constant coefficient of friction of the wetbrake and good wear protection properties are decisive for optimumlubrication. On the other hand, the thermal loading of the lubricant incomparison to the engine is not very high so that no appreciable agingof the lubricant occurs before the oil is removed from this lubricationcircuit and used for lubricating the engine. In the engine, thelubricant is then very heavily loaded in terms of thermal oxidation, anda high degree of charging with pollutants, in particular soot, occurs.

According to one preferred embodiment of the present invention there isprovision that additives are added to the lubricant removed from a unitbefore said lubricant is supplied to the unit which follows in series.Such adding of additives is expedient especially after the lubricant haspassed through the unit which is critical in terms of the coefficient offriction and in which the lubricant is particularly stressed, forexample in order to supplement additives such as antioxidants, wearprotection additives or the like, which have already been decomposed.Although all the units of a vehicle can basically be lubricated with onelubricant, the technical requirements made of these universal oils arevery high since the individual units make different requirements of thelubricant. On the one hand, for example the performance level of an HLPhydraulic oil is required for a hydraulic oil, and on the other hand,the vehicle transmission is to be supplied with a lubricant according toGL-4 or the like. In addition to these requirements for aging stability,wear protection, viscosity temperature behavior, air release capabilityand corrosion protection, wet braking and synchronizations as well asautomatic transmissions additionally produce very specific requirementsin terms of the coefficients of friction. As a result of the inventiveaddition of additives, the lubricant which is conveyed through all theunits can be optimized to the requirements of the next unit. Forexample, dispersants and detergents are essential to keep the internalcombustion engine clean, but on the other hand are not necessary in thetransmission circuit and hydraulic circuit. For example, it isconceivable to optimize an UTTO oil after use in the engine lubricationcircuit after use in the common transmission and hydraulic sump of atractor by adding dispersants, detergents and further additives, inparticular additives for protecting the engine against charging withacid combustion gases, and for protecting against the formation ofsurface coatings, mud and deposits.

The additives are preferably added directly into the oil trough of theunit or into the oil line leading to the unit, by means of an automaticdevice, metering pump or the like.

In order to avoid increased emissions after the lubricant has been burntin the engine, lubricants which are suitable for also being burnt in theengine and which are, if appropriate, treated with additives, inparticular ash-free and heavy-metal-free, low-sulfur and low-phosphorusformulations are used for lubricating the assemblies. For this purpose,in particular lubricants based on plant oils have proven suitable, itbeing possible to compensate for the aging stability of these plantlubricants, which is lower in comparison with mineral oils, byincreasing the refreshing rate.

In order to remove the used lubricant from the last unit in the series,it is possible to burn it in the engine together with the fuel. This hasthe advantage that the lubricant is also used as a fuel. In order to mixthe burnt lubricant with the fuel, the lubricant can be fed, forexample, to the fuel line, specifically preferably before the fuelfilter, in order to retain any pollutant in the used lubricant.

Alternatively to this, small quantities of waste oil can also bedisposed of by means of direct injection into the hot exhaust section ofthe internal combustion engine. Here, at temperatures of more than 500°C., auto-ignition occurs so that the waste oil burns with the impuritiescontained in it without possibly disruptive additives, particles or thelike being able to cause problems in the engine.

The burning of waste oil preferably takes place in proportion to thefuel consumption in order to keep the vehicle emissions at a constantrate. Alternatively, it is possible to provide for the waste oil also tobe burnt only in specific engine states, for example only when there isa full load or partial load of more than 70%, or to regulate therefreshing rate of the lubricant in all the units as a function of thesignal of an oil state sensor. For example, the viscosity can serve as acriterion for the oil state for a vehicle which is lubricated with alubricant which is based on rape seed oil. In this variant, therefreshing method is then activated when a specific limiting value ofthe viscosity is exceeded, by removing some of the used oil from therespective unit and replacing it with fresher oil. For other lubricantsit is also possible to use one or more other lubricant parameters toregulate the refreshing rate.

In a development of the inventive idea it is proposed-always to maintainan essentially constant quantity of lubricant in all the units involved,for example by monitoring the supply of fresh oil and discharge of wasteoil, in order to ensure that there is uniform and reliable lubrication.

The lubricant is preferably fed through the series composed of areservoir container for fresh lubricant, first to last unit to belubricated and a fuel line or exhaust section of the engine, by means ofelectric, mechanical or hydraulic metering pumps, self-venting pumpsbeing particularly preferably used. According to the invention, thepumps can both be activated and regulated individually and operated in amechanically or electronically coupled fashion. It is also possible touse electric or mechanically or hydraulically activated valves tocontrol the flow of oil for the refreshing process.

According to a further embodiment of the present invention, a fillinglevel measuring device is assigned to all the units, or to a selectionof units, which filling level measuring device can be used to controlthe corresponding metering pumps and/or valves in such a way that thevolume of oil or the oil level in the units is prevented from droppingor being exceeded. A central control device preferably regulates all thepumps, valves etc. and for this purpose evaluates all the signals of thefilling level measuring device and, if appropriate, further sensors.According to the invention, it is also possible to integrate all themetering pumps, valves and the regulating electronics which arenecessary for the described method into the on-board electronics of thevehicle, said integration permitting, for example when vehicles arefirst equipped, an integrated design of the lubrication system.Lubricant, i.e. the mixture of fresh oil and waste oil which occurs inthe units, can be continuously discharged from all the units, thismixture preferably being discharged at the point where the contaminationof the oil is highest. In this way, the highest possible degree ofpurity of the oil is always achieved in the respective unit.

The method according to the invention is suitable in principle for alltypes of vehicles, in particular for land vehicles and watercraft.Tractors, which have, as units to be lubricated, on the one hand anengine and, on the other hand, a unit composed of the assembliescomprising the hydraulics, transmission and wet brakes, constructionmachinery having the units comprising an engine, transmission andhydraulics, buses and trucks having the units comprising an engine,transmission and retarder, passenger cars, ships and boats having aseparate transmission circuit and engine oil circuit as well as fixedengines with a common coolant circuit and engine oil circuit are citedby way of example as application examples, in a non-restrictive fashion.

One particular advantage of the method according to the invention isthat the structural measures which are necessary for it can be takeninto account not only when new vehicles are manufactured but can also becorrespondingly retrofitted in used vehicles.

A further object of the present invention is a vehicle which is suitablein particular for carrying out the method described above and which hasan internal combustion engine.

According to the invention, the vehicle with internal combustion enginehas a reservoir container for fresh lubricant, at least two units to belubricated, each unit comprising one or more assemblies and having anoil trough, a fuel tank and a fuel line for feeding fuel into theinternal combustion engine, at least two of the units being arranged ina series in such a way that a feed line for fresh lubricant leads fromthe reservoir container to the first assembly in the series, a lubricantline leads in each case from the unit arranged in the preceding positionin the series to the unit arranged afterwards in the series, and adischarge line for used lubricant leads into the fuel line or theexhaust section of the internal combustion engine from the last unit inthe series.

According to one particular embodiment of the present invention, thevehicle additionally has at least one additive tank from which anadditive line leads into a lubricant line which leads to at least oneunit, or alternatively leads directly into the oil trough of a unit. Bymeans of the metered addition of additives, the lubricant which isconveyed through all the units can be optimized to the requirements ofthe corresponding units.

In one development of the inventive idea, it is also proposed to equipat least one of the lubricant lines with a metering pump via which thelubricant is fed through the corresponding lubricant line.

In addition, at least one of the units can have an automatic fillinglevel measuring device which, if appropriate via a control device, tothe metering pump or pumps, and thus permits the refreshing rate to becontrolled and the lubricant filling level in the individual units to becontrolled.

In addition or alternatively to the at least one automatic filling levelmeasurement device it is possible to provide, also for controlling therefreshing rate, an oil state sensor which is connected, if appropriatevia a control device, to the metering pump or pumps and thus permits therefreshing rate to be controlled as a function of the lubricant quality.

According to one particular embodiment of the present invention, thevehicle has a central control device which evaluates the measured valuesof the or of the filling level measuring device and/or oil state sensorsand converts them into a control signal by means of which the meteringpump or metering pumps are controlled. Moreover, the control device canbe connected to the on-board electronics or other vehicle components insuch a way in order to call additional information there, for exampleload, engine speed, oil temperatures, current fuel consumption, and touse this information to control the metering pump or metering pumps.

Further objectives, features, advantages and application possibilitiesof the invention emerge from the following description of exemplaryembodiments with reference to the drawing. Here, all the featuresdescribed and/or illustrated graphically form, in themselves or in anydesired combination, the subject-matter of the invention, evenindependently of their combination in individual claims or their backreference.

The single figure is an exemplary schematic view of a vehicle forcarrying out the method.

The vehicle has a reservoir container 1 for fresh lubricant, an additivetank 2 and three units 3 a, 3 b and 3 c to be lubricated, the unit 3 awhich is arranged first in the series being, for example, thehydraulics, the second unit 3 b being the transmission and the thirdunit being the engine 3 c. All three units 3 a, 3 b and 3 c arelubricated by circulation lubrication, the lubricant collecting in therespective oil troughs 4 a, 4 b, 4 c after it passes through thelubrication points.

A lubrication line 5 a which is equipped with a metering pump 6 a leadsfrom the reservoir container 1 to the first unit 3 a in the series,through which line fresh lubricant can be continuously ordiscontinuously fed to said first unit 3 a. In addition, the first unit4 a is connected to the second unit 4 b, and the second unit 4 b isconnected to the third unit 4 c, in each case via a lubricant line 5 b,5 c which is equipped with a metering pump 6 b, 6 c and through whichlubricant can be fed from the respectively preceding unit 4 a, 4 b tothe respectively following unit 4 b, 4 c. Finally, the lubricantdischarge line 5 d which is equipped with a metering pump 6 d leads fromthe third unit 4 c either into the exhaust section of the engine 7 orinto the fuel line (not illustrated in the drawing) in order to burn theextracted, used lubricant in the engine. While the lubricant lines 5 b,5 c and 5 d open, with their removal side, into the bottom of therespective oil troughs 4 a, 4 b and 4 c so that as far as possibleselectively used lubricant is extracted from the units 3 a, 3 b and 3 c,the supply sides of the lubricant lines 5 a, 5 b and 5 c each open intoa region which is spatially separate there from, for example at a pointwhich is arranged above the lubrication points, in order to prevent asfar as possible fresh lubricant, or lubricant which has been subjectedto little aging, being removed from the units 3 a, 3 b and 3 c throughthe lubricant lines 5 b, 5 c and 5 d. Furthermore, an additive line 8which leads from the additive tank 2 to the lubricant line 5 c whichconnects the second and third units 4 b, 4 c is provided and it can beused by the metering pump 9 to pump additives into the third unit 3 cvia the line 5 c.

In the oil trough or the oil sump (4 a, 4 b and 4 c) of the units 3 a, 3b and 3 c, in each case a filling level measuring device 10 a, 10 b and10 c is provided, which devices are connected via control lines 11 to acentral control device 12. The control device 12 receives the fillinglevel signals of all the units via the control lines 11 and can alsocontrol the metering pumps 6 a, 6 b, 6 c and the additive pumps 9 viacontrol lines 11 in such a way that the oil level and the additivecontent in the units always correspond to the necessary level. If, forexample, the oil level in unit 3 b drops below the defined minimumvalue, the metering pumps 6 a and 6 b receive a corresponding controlsignal for the continued supply of lubricant until the oil level in theunit 4 b corresponds to the set point level again. As a result, manualmonitoring of the oil level in the individual units becomes superfluous.The oil change of all the individual units which has to be carried outat periodic intervals and which is necessary with conventionallubrication is also eliminated so that only the content of the fresh oilsupply container 1 and, if appropriate, of the additive tank 2 has to beregularly replaced. For this purpose, a level monitoring system (notillustrated) can be provided in the two reservoir containers 1 and 2.

In addition to the filling level, the refreshing of the oil in theindividual units 3 a, 3 b and 3 c is also regulated by means of thecontrol device 12 in that a quantity of oil which corresponds to therefreshing rate is removed from the unit 3 c by means of the meteringpump 6 d, and the oil level in all the units is adjusted with themetering pumps 6 a, 6 b and 6 c, and the corresponding quantity ofadditive is fed to the unit 3 c via the metering pump 9. In general,small quantities of oil are removed continuously or quasi-continuouslyfrom the units 3 a, 3 b and 3 c for refreshing in order to keep thefluctuations in the filling level as small as possible. The refreshingrate can be constant over time here or be regulated as a function ofvarious influencing variables. For example, the quantity of waste oilwhich is burnt with the fuel can be set in proportion to the fuelconsumption in that the current fuel consumption is signaled to thecontrol device 12 by the injection pump or the motor vehicle on-boardelectronics via a control line (not illustrated). It is also possible tocarry out adaptation to the load state of the units in this way.Alternatively or in addition to this, oil state sensors 13 a, 13 b and13 c may be provided in order to monitor the lubricant state in theunits 3 a, 3 b and 3 c. In this way it is possible, when a specificlimiting value for the oil state is exceeded, determined for example bymeans of a parameter such as viscosity, dielectric constant or the like,to selectively replace some of the used oil in all the units 3 a, 3 b, 3c by means of the metering pumps 6 a, 6 b, 6 c, 6 d and 8. Basically,the waste oil which is intended to burn with the fuel should be meteredinto the fuel by the control device in such a way that the stressing ofthe environment is minimized. This is preferably carried out in such away that the used lubricant is continuously metered into the fuel up toa maximum proportion at which permissible emission values are not yetexceeded. A buffer tank may be provided for buffering an excess of usedlubricant which occurs under certain circumstances for a brief time.

LIST OF REFERENCE SYMBOLS

-   1 Reservoir container for fresh lubricant-   2 Additive tank-   3 a–c Unit-   4 a–c Oil trough-   5 a–d Lubricant line-   6 a–d Metering pump of the lubricant line-   7 Exhaust section of the engine-   8 Additive line-   9 Metering pump for adding additives-   10 a–c Filling level measuring device-   11 Control line-   12 Control device-   13 a–c Oil state sensor

1. A method for lubricating at least two units of a vehicle having aninternal combustion engine, each unit comprising one or more assemblies,the method comprising: successively conveying lubricant through the atleast two units including a first unit, in that fresh lubricant is fedto the first unit from a container, at least some of the lubricant, usedfor lubricating at least one assembly of the first unit, is removed froman oil trough of the first unit and is fed to a consecutive unit whichis respectively arranged afterwards in the series, wherein theconsecutive comprises at least one assembly being lubricated by thelubricant being conveyed by a previous unit; and feeding the lubricantwhich is removed from the oil trough of a last unit to the internalcombustion engine for combustion or feeding or spraying the lubricantinto the exhaust section of the engine for combustion of the lubricant,wherein the first unit to which the lubricant is fed comprises one ormore assemblies selected from the group consisting of hydraulics,transmission, and wet brakes.
 2. The method as claimed in claim 1,wherein the refreshing rate of lubricant is 0.1% to 2.5% with respect tothe fuel consumption.
 3. The method as claimed in claim 1, wherein theunits are arranged in accordance with the degree of their requirementfor purity of the lubricant.
 4. A method for lubricating at least twounits of a vehicle having an internal combustion engine, each unitcomprising one or more assemblies, the method comprising: successivelyconveying lubricant through the at least two units in that freshlubricant is fed to a first unit of the at least two units from acontainer, at least some of the used lubricant is removed from an oiltrough of the individual units and is fed to the unit which isrespectively arranged afterwards in the series; and feeding thelubricant which is removed from the oil trough of the last unit to theinternal combustion engine for combustion, wherein additives are addedto the lubricant removed from the unit, before it is fed to the unitwhich follows in the series.
 5. The method as claimed in claim 4,wherein the additives are input directly into the oil trough of the unitor into the lubricant line which leads to the unit.
 6. The method asclaimed in claim 1, wherein ash-free and heavy-metal-free, sulfur-freeand low-phosphorus formulations on the basis of plant oils are used aslubricants.
 7. The method as claimed in claim 1, wherein the lubricantwhich is removed from the oil trough of the last unit is burnt in theengine, together with fuel supplied from a fuel tank.
 8. A method forlubricating at least two units of a vehicle having an internalcombustion engine, each unit comprising one or more assemblies, themethod comprising: successively conveying lubricant through the at leasttwo units in that fresh lubricant is fed to a first unit of the at leasttwo units from a container, at least some of the used lubricant isremoved from an oil trough of the individual units and is fed to theunit which is respectively arranged afterwards in the series; andfeeding the lubricant which is removed from the oil trough of the lastunit to the internal combustion engine for combustion, wherein thelubricant which is removed from the oil trough of the last unit is fed,or sprayed, for the purposes of combustion, into the exhaust section ofthe engine.
 9. The method as claimed in claim 1, wherein the lubricantwhich is removed from the last unit is burnt in the engine, at leastessentially in proportion to the fuel consumption.
 10. The method asclaimed in claim 1, wherein the lubricant which is removed from the lastunit is burnt in the engine only when there is a full load or partialload of more than 70% of the engine.
 11. The method as claimed in claim1, wherein an essentially constant quantity of lubricant is continuouslymaintained in the units affected.
 12. The method as claimed in claim 1,wherein the lubricant is fed through the series composed of thereservoir container for fresh lubricant, first to last unit to belubricated, and the fuel line or the exhaust section of the engine, bymeans of electric, mechanical or hydraulic metering pumps.
 13. Themethod as claimed in claim 1, wherein the corresponding metering pumpsare controlled by a control device which receives and evaluates signalsof filling level measuring devices, in such a way that the lubricantlevel in the units is prevented from dropping or being exceeded.
 14. Avehicle having an internal combustion engine, having a reservoircontainer for fresh lubricant, the vehicle comprising: at least twounits to be lubricated by lubricant successively conveyed through the atleast two units, each unit comprising one or more assemblies and havingan oil trough, and a fuel tank and a fuel line for feeding fuel into theinternal combustion engine, wherein the at least two units are arrangedin series in such a way that a feed line for fresh lubricant leads fromthe reservoir container to a first unit in a series, in each case alubricant line leads from a unit which is arranged in a precedingposition in the series, to a unit which is arranged afterwards in theseries, and a discharge line for used lubricant leads into the fuel lineor an exhaust section of the internal combustion engine from the unitwhich is last in the series, wherein the first unit to which lubricantis fed comprises one or more assemblies from the group consisting ofhydraulics, transmission, and wet brakes, and wherein each consecutiveunit comprises at least one assembly being lubricated by the lubricantconveyed from an oil trough of a preceding unit.
 15. The vehicle asclaimed in claim 14, wherein an additive tank is provided, from which anadditive line leads into a lubricant line which leads to at least oneunit, or into the oil trough of a unit.
 16. The vehicle as claimed inclaim 14, wherein at least one of the lubricant lines is equipped with ametering pump.
 17. The vehicle as claimed in claim 16, wherein at leastone of the units has an automatic fuel level measuring device which isconnected, via a control device, to the metering pump.
 18. The vehicleas claimed in claim 16, wherein at least one of the units has an oillevel sensor which is connected, via a control device, to the meteringpump.
 19. The vehicle as claimed in claim 16, wherein a central controldevice is provided which evaluates the measured values of a fillinglevel measuring device and/or of oil state sensors and converts theminto a control signal by means of which the metering pump is controlled.20. The vehicle as claimed in claim 19, wherein the control device isconfigured in such a way that additional information such as load,engine speed, oil temperatures, current fuel consumption, can bereceived from the on-board electronics or other vehicle components andis used to control the metering pump.